The sensor draws about 1mA in standby mode (initiated by sensor.sleep) to keep the SSCB/I2C block powered. To get under 1mA, you need to power down the sensor but the FW doesn't have a function for that yet, I'll add it to the next release.
For now I attached a modified FW image with sensor.sleep pulling PWDN pin high (powering down the sensor), please give it a try and let us know the current consumption.

Not that example is outdated, we use machine module now (pyb.standby() == machine.deepsleep()). Also you don't need to lower the CPU frequency, in standby mode the CPU is shutdown.

I don't have an accurate meter, mine is limited to 1mA. When I use this firmware the current drops to 0 (so it's less than 1mA). Can you make sure you uploaded the modified fw ? Firmware Version should be 3.1.0

I executed the bootloader from OpenMV IDE with the firmware you sended me.
At the bottom right of the OpenMV IDE, i have the firmware version equal to 3.1.0.
The consumption is still more than 1mA (1.6mA).

The code has not changed.

I should get something around 3.4uA for STM32 + 10-20uA for OV7725 + 260-510uA for BD33IA = 275-535uA
As you said there is 1mA for SCCB standby of the camera.

For information, i remaked the current consumption changes after using sensor.sleep():
for example :

This disables the internal core regulator, I know it doesn't make sense but it seems to work.

Note sensor.sleep pulls PWDN high regardless of the argument (True or False), so you shouldn't use it if you want the sensor working. It's all a hack for now I'll add functions for this in the next release.

I also noticed the power consumption varies (I think it depends on the temperature), so a longer RTC wake up time allows the temp to drop down and the consumption. So here's the full example I'm using, measured ~500uA with this: